A typical active-matrix liquid crystal display device is constructed of two glass substrates fixed to face each other, with liquid crystal being sealed in the gap between them. A transparent common electrode is formed on one of the glass substrates. On the other glass substrate is formed a matrix of many transparent pixel electrodes. Also, circuits are formed which individually apply voltage to the pixel electrodes.
In the liquid crystal display device, the above structure is sandwiched between polarizers to produce a display. Narrow viewing angle properties are therefore one of features of the liquid crystal display device.
To widen the viewing angle properties, liquid crystal display devices are suggested which employ IPS (in-plane switching), MVA (multi-domain vertically aligned), ASV (advance super view), and other modes as physical methods such as divisional alignment.
These liquid crystal display devices with widened viewing angle properties are not applicable to mobile phone and like devices which could allow people beside the user to view the display. Therefore, liquid crystal display devices with narrow viewing angle properties are generally used in such applications.
Meanwhile, recent models of mobile phones not only have telephone and text messaging functions, but also feature image capturing (integrated camera system) and TV broadcast reception. Demands on the display device are changing.
For example, if one uses his mobile phone to make a phone call or send an email, he would want no other people to view the display content on the screen and need a display device with narrow viewing angle properties. On the other hand, when he takes a picture or watches TV, he would neither care about other people viewing the display content on the screen nor need a display device with narrow viewing angle properties. To share the content with other people, he would need a display device with wide viewing angle properties.
To sum it up, with a growing number of functions crammed into the mobile phone, there occurs a need for switching the display device between different sets of viewing angle properties (wide viewing angle properties and narrow viewing angle properties) in accordance with the functions.
Japanese published patent application 10-153968/1998 (“Tokukaihei 10-153968;” published on Jun. 9, 1998), among others, discloses a liquid crystal display device capable of, where necessary, switching the display screen between different sets of viewing angle properties. To achieve the switching, the display device exploits the viewing angle properties of the liquid crystal.
To switch between wide viewing angle properties and narrow viewing angle properties, the Tokukaihei 10-153968 liquid crystal display device divides each pixel into two pixel regions and applies the same drive voltage to the two pixel regions. The grayscale level at oblique viewing angles is thus inverted to obtain narrow viewing angle properties. Applying different drive voltages to the two pixel regions restrain the inversion of the grayscale level at oblique viewing angles to obtain wide viewing angle properties.
However, the Tokukaihei 10-153968 liquid crystal display device still has problems. The display device switchably supplies drive voltages to the two pixel regions in each pixel. The driving control of the liquid crystal display device becomes complex. The circuitry implementing the control also becomes complex.